On 25 May 2004 11:56:22 GMT, Don Johnstone
wrote:

I do not know that it is silly. On the one hand we
have a barograph which by admission is in-accurate
and requires complicated and, it has to be said, approximate
corrections and on the other hand we have GPS which
is more accurate and the corrections for which are
straightforward. My FR is also a barograph, it records
pressure altitude and the GPS altitude. Why, instead
of making a calculation to correct the pressure altitude
to geometric altitude, cannot the geometric altitude
recorded be used directly. IF not is there a cogent
argument against?

Sorry, maybe I didn't make myself clear enough. As we sometimes say in
Oz " blind Freddie can see that".


GPS altitude is now so obviously much better there should not even be
an argument.
All gliding badges, records etc are essentially trivial, of interest
mainly to the holder, with no implications for the wider world.
We have gone to ridiculous lengths to protect the integrity of
something that isn't that valuable in the first place and the security
of the approved IGC FR's is largely illusory for anyone that cares to
look carefully.

When GPS was allowed instead of turnpoint photography for records the
field wasn't level between old and new so I don't think changing to
GPS altitude for badges and records should be a philosophical or
fairness problem. The accuracy characteristics of the GPS signal are
so well known that it only remains to choose the level of confidence
you want and there is your error band.

In aviation, pressure altitude is mainly of use for air traffic
separation purposes

Mike Borgelt